Herpes-simplex virus (HS) type 1 is the etiological agent of herpes labialis and there is a correlation between HSV infections and the development of certain neoplastic diseases. HSV induces approximately 50 polypeptides, some of which possess enzymatic activity, in permissively infected cells. However except for the HSV encoded DNA polymerase the role of these polypeptides in HSV replication, recombination transformation, and latency is unknown. The goals of this research are to determine the function of a HSV specified deoxyuridine triphosphate nucleotidohydrolase (dUTPase) in HSV replication and recombination and to determine the dUTPase's potential role in affecting the activity of specific antiviral agents used in the treatment of infections caused by HSV. The effect of increased deoxyuridine (dUdr) incorporation into HSV DNA on viral replication, recombination and mutagenesis will be determined using HSV mutants which are defective in dUTPase activity. We will quantitate the amount of dUdr that is incorporated into the DNA of these mutants, determine what effect increased dUdr incorporation into the DNA has on the infectivity of the viral DNA, determine the mutation frequency in these dUTPase(-) mutants to bromodeoxyuridine and phosphonoacetic acid, determine the recombination frequency in the dUTPase(-) mutants relative to the DNA polymerase and thymidine kinase structural genes and we will determine the map location of the structural gene for the HSV encoded dUTPase. We will also determine the potential role of the HSV specified dUTPase in affecting the activity of specific antiviral compounds by determining in vivo the sensitivity of the dUTPase(-) mutants to specific thymidine (deoxyuridine) analogs and by determining in vitro whether the triphosphate derivitives of these analogs can act as alternative substrates for the cellular and/or HSV specified dUTPases. These studies will not only provide an insite into the function of the HSV-specified dUTPase in virus replication but they should provide a mechanism that will allow for the rational development of agents that can be employed for antiviral therapy. Also these studies may demonstrate that the dUTPase- mutants can be use for developing a screening test for the detection of potential antiviral agents.